Well, registration is done through Amazon webservice, so it's not just some piece of data on Kindle, it's also a record at Amazon. I think you have to go through this process if you really want you Kindle to be registered - no amount of local hacking will do this.

As far as I can tell, there is very little on Kindle which is device specific - serial number written in NOR flash, SSL client certificate signed by Amazon (probably Kindle downloads it during registration process) and some simple text file that tells UI that Kindle is indeed registered.